[0001] This invention relates to a method and an apparatus for treating a waste gas, and
more specifically to an apparatus for treating a waste gas by discharge plasma. More
particularly, this invention relates to a waste gas treating device for treating reactive
gases discharged from various semi-conductor production facilities in various thin
film forming techniques utilizing reduced pressures (such as chemical vapor deposition
method, or plasma CVD method), an oxidation technique utilizing reduced pressures,
a diffusion technique, and a dry etching technique, with plasma under reduced pressures
to render them non-toxic irrespective of their amount.
[0002] There are a variety of gases which are used in various semiconductor production facilities
for thin film formation under reduced pressures, oxidation and diffusion and dry etching.
In particular, reactive gases are not always completely consumed in the respective
facilities, and are discharged as unreacted gases or as mixtures with by-product gases
occurring at the time of semi-conductor production, through a vacuum discharging system.
[0003] Many of these gases have combustibility and explosiveness or toxicity, and then they
are released without treatment, they may be the cause of disaster or pollution. Hence,
the allowable concentrations of these gases in the atmosphere are prescribed.
[0004] Methods used heretofore to render these gases non-pollutional include a chemical
treatment involving a catalyzed reaction, absorption and adsorption by means of a
scrubber, or a dry adsorption by using various adsorbents. Gases which are likely
to have a danger of burning or explosion are released after they are diluted with
a large amount of an inert gas.
[0005] The above methods are all performed at ordinary pressures. They are not effective
means against safety in a pressure reduction piping portion including a vacuum discharge
facilities or in an ordinary pressure piping section leading to an atmospheric pressure
treating facilities, some examples of accidents have been reported.
[0006] On the other hand, as a treating method under reduced pressures, there have been
proposed methods of using discharge to treat a waste gas non-pollutional. These methods
are characterized in that as against the aforesaid treatment under ordinary pressures,
gases to be treated are treated under reduced pressure before they reach the vacuum
discharge facilities. For example, Japanese Laid-Open Patent Publication No. 129868/1976
discloses that by reacting a waste gas containing a toxic substance with an oxidizing
agent in a plasma space, the toxic substance is converted into a stable compound and
removed from the waste gas. Furthermore, Japanese Laid-Open Patent No. 6231/1983 describes
a waste gas treating apparatus for decomposing a waste gas with a discharge plasma
and discharging it. However, the treating methods utilizing discharge have some problems
and no practical utility can be found because with these methods, it is difficult
to maintain a stable state of plasma under varied loadings, especially under varied
pressure, and there is a limit in the range of application.
[0007] In recent years, a method utilizing plasma on which a magnetic field is superimposed
(magnetic field superimposing method) was proposed as a means of maintaining a stable
plasma state even under varied pressures (Society of Applied Physics, Meetings for
the Study of Plasma Electronics, January 1986). In this magnetic field superimpositing
method, a direct current or an alternating current magnetic field is applied at an
angle of about 45° to about 135° with respect to the direction of a magnetic field
formed by an electrode. As a result, the radius of pivoting of an electron in a plasma
becomes small, and the electron can pivot between the electrodes, and a stable plasma
can be maintained under varied pressures ranging from 0.01 m torr to several tens
of torr.
[0008] The waste gas treatment utilizing discharge must be carried out as above under reduced
pressure before it leads to a vacuum discharge facilities. Necessarily, the waste
gas treating apparatus is arranged between each semiconductor production facilities
and a vacuum discharge facilities. Accordingly, in order to use the treatment under
reduced pressures actually for practical utility the treating device should be easily
incorporated between these facilities while maintaining its treating ability, and
the gas flow passages inside the treating apparatus should have such a structure as
to suppress the decrease in the discharge conductance utmost. The prior art, however,
proposed only conceptional methods or apparatus which fulfill such necessary conditions
for realizing such practical utility. A practical waste gas treating apparatus has
not yet come into acceptance.
[0009] Preferred embodiments of this invention may fully satisfy necessary conditions for
realizing an apparatus having utility, and realize a treating apparatus by using discharge
which can maintain a stable treating ability over a long period of time.
[0010] The present inventors extensively made investigations, and found, that by disposing
cathodes opposite to each other and anodes opposite to each other so as to form a
space defined by an anode pair and a cathode pair, and constructing a part or the
whole of the anodes and cathodes from a plurality of plates or pillars, and applying
a magnetic field in the direction opposite to the cathodes, the capacity of the treating
apparatus which treats the gas per unit volume can be increased very much and the
treating apparatus can be stably operated over a long period of time.
[0011] EP-A-343987 and the corresponding application JP-A-1-297126 were published after
the priority date of the present application, and thus EP-A-343987 is prior art only
by virtue of Article 51(3) EPC, so that it is relevant only to novelty.
[0012] It discloses apparatus for waste gas treatment having a discharge tube containing
an opposed pair of anodes and, at right angles thereto, an opposed pair of cathodes.
Magnetic field means apply a magnetic field in the direction in which cathodes are
opposed. There may be auxiliary anodes in the form of rows of elongate elements.
[0013] According to the present invention, there is provided apparatus for treating a waste
gas including a discharge tube having a gas flow passage; electrodes located in the
flow passage for creating a discharge plasma; electrical power supply means connected
to said electrodes; and magnetic field means for applying a magnetic field across
the gas flow passage; and wherein said electrodes comprise first and second anode
plate means spaced apart so as to confront each other across said flow passage; and
first and second cathode plate means spaced apart so as to confront each other across
said flow passage and extending substantially at right angles to the anode plate means;
a part or a whole of said anode and cathode plate means being constituted by a respective
multiplicity of plates or pillars disposed in a row so as to define a plate portion,
of a respective plate means, the plates or pillars of a cathode plate means or an
anode plate means being electroconductively connected to each other and to the power
supply means; and wherein said magnetic field means is arranged to apply a magnetic
field which extends in the direction in which the cathode plate means are opposed.
[0014] In a second aspect the invention provides a method of treating a waste gas by passing
it through a discharge tube of such an apparatus and subjecting it to the discharge
plasma.
[0015] The present invention will be described below in detail.
[0016] The gases to be used in this invention may be gases or vapors which are discharged
from various semi-conductor production facilities and when released into the atmosphere
without treatment, may possibly cause some disaster or pollution. In particular, they
cannot be completely treated by conventional catalyzed reactions and such means as
absorption and adsorption. Examples of such gases applicable to this invention include
silane-type gases such as monosilane and disilane; alkylsilane-type gases such as
monomethylsilane and dimethylsilane; germanium-type gases; chlorosilane-type gases;
fluoro silane-type gases; mixed gases containing doping gases, such as phosphine and
diborane; and tetraethoxysilanes (TEOS) which have been recently spotlighted as a
material for an insulated oxidized film. These are not the only examples, and mixtures
of these, and those diluted with hydrogen or nitrogen may also be used in this invention.
[0017] The preferred embodiments of the invention will be described with reference to the
accompanying drawings.
[0018] Figure 1 is a horizontal section showing the basic concept of the prior art. Figures
2, 4, 5 and 7 are horizontal sections showing the embodiments of the present invention.
Figures 3 and 6 are vertical section views. Figures 2 to 6 show examples of plate-like
electrodes, and Figure 7, examples of cylindrical electrodes. Figure 3 is a sectional
view of Figure 2 taken on the line III-III, and Figure 6 is a sectional view taken
on the line VI-VI of Figure 5.
[0019] Figures 1, 2, 4, 5 and 7 are sectional views taken in a direction at right angles
to the direction of the gas flow passage. The flow of gases are either upward or downward.
[0020] In Figures 1 to 7, the reference numeral 1 represents a cathode or a cathode pair;
the reference numeral 2 represents an anode or an anode pair; the reference numeral
3 represents a permanent magnet; the reference numeral 4 represents a vacuum container;
and the reference numeral 5 represents an electrical conductor material.
[0021] Figures 8 and 9 are a vertical section view and a horizontal section showing an embodiment
of the prior art and correspond to each other.
[0022] In Figures 8 and 9, the reference numeral 1 represents a cathode or a cathode pair;
the reference numeral 2 represents an anode or an anode pair; the reference numeral
2′ represents an auxiliary anode; the reference numeral 3 represents a ferrite magnet;
the reference numeral 4 represents an insulation material; the reference numeral 5
represents a gas introduction opening; the reference numeral 6 represents a gas leading
opening; the reference numeral 8 represents a vacuum container; and the reference
numeral 9 represents a yoke. Generally, many of discharge devices have such a structure
that a cathode and an anode are opposite to each other. Since an electron linearly
goes from the cathode to the anode in such a structure, it is not easy to form a plasma
having a high strength. Furthermore, because the range of applicability to pressure
variations is narrow, restrictions are imposed on the desired waste gas treating conditions.
[0023] In contrast, the present invention as shown in Figure 1 basically may form a cathode
pair by providing a pair of cathodes opposite to each other and an anode pair by providing
a pair of anodes opposite to each other, and further superimposing a magnetic field
in the opposing direction of the cathodes. By utilizing a cyclone motion of an electron
using a magnetic line of force as an axis, electrons are trapped between the opposing
cathodes so that a plasma of very high strength can be formed. A stable plasma can
be obtained which can withstand a wide range of pressure variations in a range of
from 1 mtorr to 10 torr.
[0024] In this way, according to this invention, basically at least one pair of anodes 2
is provided opposite to each other, and at least one pair of cathodes 1 is provided
in a space including the anode pair in a direction nearly at right angles to the anodes
without contacting the anodes. Furthermore, a magnetic field is superimposed on the
opposing direction of the cathodes, and a plasma having a high strength, called a
cathode glow, is formed between the opposing cathodes. On the other hand in a space
excluding the cathode glow portion between the opposing anodes a plasma called "positive
column" is formed via a sheath. As a result, the gas to be treated is subjected to
discharge treatment.
[0025] In the discharge treatment of a waste gas directed to render most of an unreacted
gas non-toxic, for example, unlike plasma CVD etc. utilizing discharge-gas in the
thin film formation utilizing a part of the starting gas, the amount of electric power
required for the discharge treatment is extremely high. It is important to secure
an electrode area which can withstand such a large amount of electric power within
an apparatus of a limited volume. Particularly, to secure the cathode area for releasing
electrons is essential for maintaining a stable plasma state.
[0026] The present inventors found that such an arrangement of electrodes is an effective
means for increasing the electrode area so as to withstand the amount of electric
power required for the discharge treatment that an auxiliary electrode as a means
for increasing the electrode area an auxiliary electrode is disposed within a space
formed of at least one pair of cathodes and at least one pair of anodes - see EP-A-0
343 987. However, such a treating apparatus is limited in treating ability with regard
to the amount of a gas discharged from a semiconductor production facilities, and
a further increase in the electric power is required to treat a large amount of the
waste gas. This inevitably results in the necessity for increasing the electrode area.
If the above-mentioned area is not sufficiently secured, the electrodes become red-hot,
and further an arc-discharge may occur. As a result, structural damages such as electrical
deformation or thermal deformation may occur, and the treating apparatus fails to
function properly.
[0027] The above structural damages not only mean the damages of electrodes but also means
that an insulator such as tetrafluoroethylene accumulates the heat generated by forming
discharge and is thermally deformed so that the construction of the electrodes cannot
be maintained if in the case of the treating apparatus of Japanese Laid-Open Publication
No. 287126/1989.
[0028] Thus, the present inventors made extensive investigations in order to secure an electrode
area which can withstand the electric power. As a result, by constructing anodes 1
and cathodes 2 partly or wholly from a plurality of plates or pillars (or rods) and
connecting and assembling them through electrical conduction and integrating them
to form an electrode structure having the same action as the cathodes 1 and the anodes
3 shown in Figure 1. Figures 2 to 7 show examples of such integrated plate-like or
pillar-like electrode structures. In Figures 2 and 3, all of the cathodes are composed
of a plurality of plates or pillars and in Figures 5 and 7, all of the cathodes and
the anodes are composed of a plurality of plates or pillars. In the present invention,
the "electrode area" is defined as an area surrounded by the same points of potentials
on the electrodes.
[0029] In the present invention, the electrode area which can withstand the electric power
inputted is a value in which the consumed current value is not more than 20mA/cm²,
preferably not more than 10mA/cm². The distance between the plurality of plates or
pillars connected and assembled under electrical conduction as the shortest distance
between adjacent cathodes or anodes, as the shortest distance, is preferably 0.1 mm
to mm, more preferably 1 mm to 10 mm.
[0030] In the opposing cathodes, the right opposing distance may vary depending upon the
pressure and the composition of the gas to be treated, but the shortest distance between
the opposing cathodes is preferably 5 mm to 80 mm, more preferably 10 mm to 40 mm.
Furthermore, in the case of anodes which oppose the cathode pair in a direction nearly
at right angles, the shortest distance between the cathode and the anode is preferably
5 mm to 120 mm, more specifically 10 mm to 50 mm.
[0031] The material for the anode or the cathode is not particularly limited so long as
at least its surface is electrically conductive. Usually it is stainless steel. The
above cathode or anode measures 10 mm to 10000 mm in width, 100 mm to 100000 mm in
length and 0.1 mm to 5 mm in thickness. In the case of a plate, it has a width of
1 mm to 100 mm, a length of 100 mm to 100000 mm and a thickness of 0.1 mm to 5 mm.
In the case of a cylinder, a circle taken on its section is about 1 mm to 30 mm in
diameter and 100 mm to 100000 mm in length. The number of plates or pillars in one
row is not particularly limited, and may be 2 to 200, preferably 5 to 50.
[0032] In the present invention, a plurality of plates or pillars are electrically conductively
connected and integrated. Specifically, when an electric power is put on, they are
connected so that an electric current flows so that overheating leading to wire breaking
may not occur. The connecting means are arbitrary. But as shown in Figure 2, a plurality
of plates is disposed at nearly equal intervals (adjoining distances), preferably
the plates are parallel to each other, and as a whole, the plates form nearly straight
rows. These rows are preferably linked or cemented by a cylider or square pillar as
an electrically conductive materials (for example, round copper rods or stainless
steel bolts and nuts). Screwing, welding and soldering are conceivable as a means
of connection or cementing. Of course, it is possible to dispose electrically conductive
materials at the upper part of the container and suspend a plurality of plates at
nearly equal intervals from the electrically conductive materials. No particular limitations
are imposed on in this regard.
[0033] Sets of these cathodes and anodes are set up in a tubular container. The shape of
the container is not particularly limited, and it may be a cylindrical or square pillar.
The device for applying a magnetic field to form a magnetic field in the direction
directed toward the cathode may be set up either inside or out of the container, and
the magnetic field may be a direct current one or alternate current one. The magnetic
flux density to be applied is at lease 50 gausses at the lowest portion, preferably
at least 100 gausses. From the standpoint of a practical waste gas treating device,
the application device is preferably based on a ferrite sintered type magnet having
an inexpensive and simple and convenient direct current magnetic field. The use of
magnets as samarium-cobalt or neodymium-iron-boron type rare earth magnets is also
effective. The opposing direction of the cathode includes a range of about 45° to
135°. The power supply used in this invention may be a direct current or alternate
current. From the efficiency of electric power, a dc power supply is preferred.
[0034] Furthermore, in the present invention, the plasma in this invention exhibits current-voltage
characteristics which can generally be regarded as constant voltage characteristics.
To perform continuous and stable treatment of a gas, it is convenient to employ a
constant output power supply or a constant-current power supply.
[0035] To perform a waste gas treatment by using the waste gas discharge treatment device
of this invention, a gas to be treated is introduced from the gas introduction inlet
into a plasma space on which a magnetic field is superimposed, the plasma space being
defined by a magnetic field application device with a cathode pair and an anode pair.
The introduced waste gas is subjected to discharge treatment for a predetermined residence
time, and then discharged from the gas opening and released into the atmosphere via
the vacuum discharge device After discharging from the vacuum discharge device, it
may further be subjected to non-toxification treatment. The loading conditions employed
in this invention is 1 m torr to 10 torr.
[0036] The following Examples further illustrate the invention in detail.
Example 1
[0037] The same device as shown in Figures 2 and 3 was used. In a stainless steel vacuum
container having an inner capacity of 3.7 liters and including a gas introduction
opening 6 and a gas leading opening. Within the vacuum container, sixteen stainless
steel plates as cathode plates having a width of 6 mm, a length of 400 mm, and a thickness
of 2 mm (8 plates per row), two stainless steel plates having a width of 40 mm, a
length of 400 mm, and a thickness of 2 mm as anode plates were used to construct electrode
sets. At this time, adjusted the shortest distance between the opposing cathodes was
adjusted to 20 mm, and the shortest distance between the cathode and the anode was
to 25 mm. Ths shortest distance between the adjoining cathode plates was adjusted
to 6 mm. The anode plates and cathode plates were integrated as shown in Figures 2
and 3 by using a round brass rods having a diameter of 3 mm.
[0038] As a magnetic field application device, a ferrite sintered magnet having a surface
magnetic flux density of 900 gausses was used to form a dc magnetic field, and the
cathode pair and the anode pair were coupled to a dc power supply. From the gas introduction
opening, 100 % monosilane gas (100 Sccm) was introduced, and subjected to a discharge
treatment under a pressure of 0.2 torr by supplying an electric power of 850 W.
[0039] The discharge treated gas was measured by af quadrupole mass spectrometer between
the gas leading opening and the vacuum discharge facility, and the concentration of
the residual monosilane gas was 2.0 %. The test was carried out under the above conditions
with a cycle consisting of operation for 3 hours and suspension for 30 minutes. The
operation could be performed stably over 100 hours.
Comparative Example 1
[0040] The same discharge treatment as in Example 1 was carried out except that as a cathode
plate, a stainless steel plate having a width of 40 mm, a length of 400 mm and a thickness
of 2 mm was used as shown in Figure 1. Gradually, the inside of the opposing cathodes
were deformed and became red-hot, and after 30 minutes when the spark became unusual,
the treatment had to be discontinued.
Example 2
[0041] The same device as shown in Figure 4 was used. In a stainless steel container having
an inner capacity of 3.7 liters, 26 stainless steel plates having a width of 6 mm,
a length of 400 mm and a thickness of 1 mm (13 plates per row) as cathode plates and
two stainless steel plates having a width of of 37 mm, a length of 400 mm and a thickness
of 2 mm as anode plates were used to construct sets of electrodes. The shortest distance
between the opposing cathodes was adjusted to 8 mm, and the shortest distance between
the cathode and the anode, to 25 mm. The shortest distance between adjacent cathode
plates was 2 mm. These cathode and anode plates were assembled integrally by using
round copper rods having a diameter of 3 mm as shown in Figure 4 as electrically conductive
materials 5.
[0042] A dc magnetic field was formed, and the electrode sets were coupled to a dc power
supply. From the gas introduction opening, 20 % monosilane gas (250 Sccm) diluted
with nitrogen was introduced, and treated at a pressure of 0.5 torr by supplying an
electric power of 700 W. The amount of the residual monosilane gas was not more than
1 %. No abnormality occurred in the continuous treatment for 3 hours. The same cycle
text as in Example 1 was performed, but it was confirmed that no problem occurred.
Example 3
[0043] The same device as shown in Figures 5 and 6 was used. In a stainless steel vacuum
container provided with a gas introduction opening 6 and a gas leading opening 7 and
having an inner capacity of 8 liters, 36 stainless steel plates having a width of
8 mm, a length of 440 mm and a thickness of 2 mm (9 per row) as cathode plates and
18 (9 plates per row) stainless plates the same stainless steel plates were used to
construct electrode sets. The shortest distance between adjacent cathode plates was
adjusted to 4 mm, and the shortest distance between anode plates, to 9 mm. As shown
in Figure 5, the cathode plates and the anode plates were integrated by using M3 stainless
steel bolts and nuts as electrically conductive materials 5.
[0044] By using a dc magnetic field and a dc power supply, 50 % of monosilane gas (800 Sccm)
diluted with nitrogen was treated at 0.3 to 0.4 torr. As a result, the amount of the
residual monosilane gas was 2 %. At this time, the current required for the discharging
was 2200 mA. Under these conditions, the device was continuously operated for 8 hours.
No problem arose. The cycle test was performed, but no problem occurred either.
Example 4
[0045] The same device as shown in Figure 7 was used. In a stainless steel vacuum container
equipped with a gas introduction opening and a gas leading opening and having an inner
capacity of 5 liters, 25 stainless steel rods (7 per row) having a diameter of 6 mm,
a length of 350 mm as cathodes and 14 same stainless rods (7 per row) to construct
electrode sets. The shortest distance between adjacent cathodes and the shortest distance
between adjacent anodes were 3 mm. The shortest distance between the opposing cathodes
was adjusted to 10 mm, and the shortest distance between the cathode and the anode,
to 30 mm. By using a dc magnetic field and an ac power supply, 5 % tetraethoxysilane
diluted with nitrogen (500 Sccm) was subjected to discharge treatment at 0.5 torr.
As a result, the decomposition rate of tetraethoxysilane was 85 %, and a stable operation
continued for 50 hours. After the treatment, the electrodes were taken out, and it
was confirmed that a white deposit, judged to be SiO₂, formed on the surface of the
electrodes. Accordingly, it was found that ethoxysilane could be treated. Most of
the decomposition product accumulated on the bottom of the container. But it was confirmed
that this is not determinant to the operation for a suffiently long period of time.
The apparent power used for discharging was 4 KVA.
Comparative Example 2
[0046] The same device as shown in Figure 8 (i.e., in Figure 9) was used.
[0047] In a stainless steel vacuum container having an inner capacity of 2 liters equipped
with 2-inch flanges a gas introduction opening 5 and a gas leading opening 6, one
pair of stainless steel plates having a width of 20 cm, a length of 30 cm and a thickness
of 2 mm was provided in opposition to each other with an interval of 3 cm to form
a cathode pair 1, and in a space between the pair of cathodes via polytetrafluoroethylene
4 (Teflon, registered trademark) in its diameter direction, a pair of anodes was formed
by providing stainless steel plates having a width of 2 cm, a length of 30 cm and
a thickness of 2 mm to each other without contacting the anodes. Within a space including
the pair of cathodes 1 and the pair of anodes four auxiliary anodes 2′ having the
same sizes as the anodes were provided nearly parallel to the anodes. To the back
surfaces of the cathode, a ferrite magnet 3 having a surface magnetic flux density
of 500 gausses was provided via Teflon 4. By a yolk 9, a dc magnetic field was formed
in a direction opposite to the cathodes. The cathode pair and the anode pair were
connected to an ac power supply. From the gas introduction opening 3, 100 % monosilane
gas (50 Sccm) was introduced to generate a plasma. From the gas leading opening 6,
air was discharged by vacuum by a mechanical booster pump. A constant power was supplied
to the cathode, and the concentration of the residual monosilane gas was at the gas
lead-out opening was measured by a quadrupole mass spectrometer.
[0048] The concentration of the residual monosilane gas under constant conditions involving
a pressure of 0.2 torr and a supplied power of 250 W was 3.0 % when the distance between
the anodes was 10 times that between the cathodes.
[0049] According to this, there can be provided a practical waste gas discharging treatment
apparatus by which gases discharged from various semiconductor production facilities
such as monosilane gas can be treated to render them non-toxic by discharge treatment.
Accordingly, the waste gas treating apparatus of this invention contributes greatly
to treat toxic gases occurring in the production of various semiconductor devices
into nontoxic gases.
1. Apparatus for treating a waste gas including a discharge tube (4) having a gas flow
passage; electrodes (1,2) located in the flow passage for creating a discharge plasma;
electrical power supply means connected to said electrodes; and magnetic field means
(3') for applying a magnetic field across the gas flow passage; and wherein said electrodes
comprise first and second anode plate means (2) spaced apart so as to confront each
other across said flow passage; and first and second cathode plate means (1) spaced
apart so as to confront each other across said flow passage and extending substantially
at right angles to the anode plate means (2); a part or a whole of said anode and
cathode plate means (1,2) being constituted by a respective multiplicity of plates
or pillars disposed in a row so as to define a plate portion, of a respective plate
means, the plates or pillars of a cathode plate means (1) or an anode plate means
(2) being electroconductively connected to each other (5) and to the power supply
means; and wherein said magnetic field means (3) is arranged to apply a magnetic field
which extends in the direction in which the cathode plate means (1) are opposed.
2. The apparatus of claim 1 in which the cathode and anode plate means (1,2) are composed
of stainless steel.
3. The apparatus of claim 1 in which the magnetic field means (3) applies a flux density
of at least 50 gauss.
4. The apparatus of claim 1 in which the magnetic field means (3) comprises a ferrite
sintered type magnet or a rare earth magnet.
5. The apparatus according to any preceding claim wherein said first and second cathode
plate means (1) are each constituted by respective multiplicities of plates or pillars.
6. The apparatus according to claim 5 wherein said first and second anode plate means
(2) are each constituted by respective multiplicities of plates or pillars.
7. A method of treating a waste gas comprising flowing it through a discharge tube (4)
of an apparatus according to any preceding claim, and subjecting it to a discharge
plasma produced by means of said apparatus.
8. A method according to claim 7 wherein the waste gas comprises one or more of silane-type
gases, alkylsilane-type gases, germanium-type gases, chlorosilane-type gases, fluorosilane-type
gases, a mixed gas containing phosphine and diborane as a doping gas, and tetraethoxysilane
gas.
9. A method according to claim 7 in which the current consumption of the electrodes (1,2)
is not more than 20 mA/cm² of cathode area.
10. A method according to claim 7 in which the gas is treated at a pressure of 1 mtorr
to 10 torr (0.13-1300 Nm⁻²).
11. A method according to any of claims 7 to 10 wherein the magnetic field means applies
a flux density of at least 50 gauss.
12. A method according to any of claims 7 to 11 wherein the waste gas is selected from
monosilane, disilane and mixtures thereof; or from monomethylsilane, dimethylsilane
and mixtures thereof.
13. A method according to any of claims 7 to 12 wherein the waste gas is diluted with
hydrogen or nitrogen.
1. Vorrichtung zur Behandlung eines Abgases, umfassend ein Entladungsrohr (4) mit einem
Gasflußdurchgang; im Flußdurchgang angeordnete Elektroden (1,2) zur Erzeugung eines
Entladungsplasmas; eine an die genannten Elektroden angeschlossene Stromzufuhreinrichtung;
und eine Magnetfeldeinrichtung (3') zum Anlegen eines Magnetfeldes über den Gasflußdurchgang
hinweg; und worin die genannten Elektroden eine erste und eine zweite Anodenplatte
(2), die im Abstand voneinander so angeordnet sind, daß sie einander über den genannten
Flußdurchgang hinweg gegenüberstehen; und eine erste und eine zweite Kathodenplatte
(1), die im Abstand voneinander so angeordnet sind, daß sie einander über den genannten
Flußdurchgang hinweg gegenüberstehen und sich im wesentlichen im rechten Winkel zu
den Anodenplatten (2) erstrecken; wobei ein Teil der oder die gesamten Anoden- und
Kathodenplatten (1,2) aus einer jeweiligen Vielzahl von Platten oder Pfeilern bestehen,
die in einer Reihe so angeordnet sind, daß sie einen Plattenabschnitt einer jeweiligen
Platte definieren, wobei die Platten oder Pfeiler einer Kathodenplatte (1) oder einer
Anodenplatte (2) miteinander (5) und mit der Stromzufuhreinrichtung elektrisch leitend
verbunden sind; und worin die genannte Magnetfeldeinrichtung (3) so angeordnet ist,
daß ein Magnetfeld angelegt wird, das sich in die Richtung erstreckt, in der die Kathodenplatten
(1) einander gegenüberstehen.
2. Vorrichtung nach Anspruch 1, bei der die Kathoden- und Anodenplatten (1,2) aus rostfreiem
Stahl bestehen.
3. Vorrichtung nach Anspruch 1, bei der die Magnetfeldeinrichtung (3) eine Flußdichte
von zumindest 50 Gauß anlegt.
4. Vorrichtung nach Anspruch 1, bei der die Magnetfeldeinrichtung (3) einen Magneten
vom Sinterferrittyp oder einen Seltenerdmagneten umfaßt.
5. Vorrichtung nach einem der vorhergehenden Ansprüche, worin die genannte erste und
zweite Kathodenplatte (1) jeweils aus einer Vielzahl von Platten oder Pfeilern bestehen.
6. Vorrichtung nach Anspruch 5, worin die genannte erste und zweite Anodenplatte (2)
jeweils aus einer Vielzahl von Platten oder Pfeilern bestehen.
7. Verfahren zur Behandlung eines Abgases, bei dem es durch ein Entladungsrohr (4) einer
Vorrichtung nach einem der vorhergehenden Ansprüche hindurchströmen gelassen und einem
durch die genannte Vorrichtung erzeugten Entladungsplasma unterworfen wird.
8. Verfahren nach Anspruch 7, worin das Abgas eines oder mehrere aus Silantypgasen, Alkylsilantypgasen,
Germaniumtypgasen, Chlorsilantypgasen, Fluorsilantypgasen, ein Mischgas, das Phosphin
und Diboran als ein Dotierungsgas enthält, und Tetraäthoxysilangas umfaßt.
9. Verfahren nach Anspruch 7, bei dem der Stromverbrauch der Elektroden (1,2) nicht mehr
als 20 mA pro cm² Kathodenfläche beträgt.
10. Verfahren nach Anspruch 7, bei dem das Gas mit einem Druck von 1 mTorr bis 10 Torr
(0,13-1300 Nm⁻²) behandelt wird.
11. Verfahren nach einem der Ansprüche 7 bis 10, worin die Magnetfeldeinrichtung eine
Flußdichte von zumindest 50 Gauß anlegt.
12. Verfahren nach einem der Ansprüche 7 bis 11, worin das Abgas aus Monosilan, Disilan
und Mischungen daraus; oder aus Monomethylsilan, Dimethylsilan und Mischungen daraus
ausgewählt ist.
13. Verfahren nach einem der Ansprüch 7 bis 12, worin das Abgas mit Wasserstoff oder Stickstoff
verdünnt wird.
1. Appareil pour traiter un gaz perdu, comprenant un tube de décharge (4) ayant une voie
de passage d'écoulement de gaz ; des électrodes (1, 2) situées dans la voie de passage
d'écoulement pour créer un plasma de décharge ; des moyens de fourniture de puissance
électrique connectés auxdites électrodes ; et des moyens générateurs de champ magnétique
(3') pour appliquer un champ magnétique en travers de la voie de passage d'écoulement
de gaz ; et dans lequel lesdites électrodes comprennent des moyens (2) formant des
première et seconde plaques anode espacées l'une de l'autre de façon à être mutuellement
en regard en travers de ladite voie de passage d'écoulement ; et des moyens (1) formant
des première et seconde plaques cathode espacées l'une de l'autre de façon à être
mutuellement en regard en travers de ladite voie de passage d'écoulement et s'étendant
sensiblement perpendiculairement aux moyens (2) formant plaques anode ; une partie
ou la totalité desdits moyens (1, 2) formant plaques anode et cathode étant constituée
par une multiplicité respective de plaques ou de colonnes disposées en une rangée,
de façon à définir une portion formant plaque d'un moyen respectif formant plaque,
les plaques ou colonnes d'un moyen formant plaque cathode (1) ou d'un moyen formant
plaque anode (2) étant connectées de façon électroconductrice l'une à l'autre (5)
et au moyen de fourniture de puissance ; et dans lequel ledit moyen générateur de
champ magnétique (3) est agencé pour appliquer un champ magnétique qui s'étend dans
la direction suivant laquelle les moyens formant plaques cathode (1) sont opposés.
2. L'appareil de la revendication 1, dans lequel les moyens formant plaques cathode et
anode (1, 2) sont composés d'acier inoxydable.
3. L'appareil de la revendication 1, dans lequel le moyen générateur de champ magnétique
(3) applique une densité de flux d'au moins 50 gauss.
4. L'appareil de la revendication 1, dans lequel le moyen générateur de champ magnétique
(3) comprend un aimant du type fritté en ferrite ou un aimant en métal des terres
rares.
5. L'appareil selon toute revendication précédente, dans lequel lesdits moyens formant
première et seconde plaques cathode (1) sont constitués chacun par des multiplicités
respectives de plaques ou de colonnes.
6. L'appareil selon la revendication 5, dans lequel lesdits moyens formant première et
seconde plaques anode (2) sont constitués chacun par des multiplicités respectives
de plaques ou de colonnes.
7. Un procédé de traitement d'un gaz perdu consistant à le faire s'écouler à travers
un tube de décharge (4) d'un appareil conforme à toute revendication précédente et
à le soumettre à un plasma de décharge produit au moyen dudit appareil.
8. Un procédé selon la revendication 7, dans lequel le gaz perdu comprend un ou plusieurs
gaz des types suivants : gaz du type silane, gaz du type alcoylsilane, gaz du type
germanium, gaz du type chlorosilane, gaz du type fluorosilane, un gaz mixte contenant
de la phosphine et du diborane comme gaz dopant, et gaz tétraéthoxysilane.
9. Un procédé selon la revendication 7, dans lequel la consommation de courant des électrodes
(1, 2) n'est pas supérieure à 20 mA/cm² de surface de cathode.
10. Un procédé selon la revendication 7, dans lequel le gaz est traité à une pression
de 1 mTorr à 10 Torr (O,13-1300 Nm⁻²).
11. Un procédé selon l'une des revendications 7 à 10, dans lequel le moyen générateur
de champ magnétique applique une densité de flux d'au moins 50 gauss.
12. Un procédé selon l'une des revendications 7 à 11, dans lequel le gaz perdu est choisi
parmi le monosilane, le disilane et des mélanges de ceux-ci ; ou parmi le monométhylsilane,
le diméthylsilane et des mélanges de ceux-ci.
13. Un procédé selon l'une des revendications 7 à 12, dans lequel le gaz perdu est dilué
avec de l'hydrogène ou de l'azote.